This organization is formed to co-operate in research on malignant disease in children; specifically to study the factors which may cause or influence these diseases, and to develop, evaluate and improve methods of treatment. The primary objective of the co-operative group has been the evaluation of new biological and chemotherapeutic agents in the treatment of acute leukemia and solid tumors in childhood, and to find new and better ways of using the already known agents. It is also our objective to provide supportive care for these children with leukemia and solid tumors while they are on protocol studies and to evaluate the effect of this supportive care on their longevity and their well-being while on study. This supportive care includes medical supportive care (platelet transfusions) and financial supportive care (domiciliary care and out-patient care), and social service assistance.